Metal layers on a wide variety of substrates are used for applications in the electronics and electrical industry. Electroless metal plating is a valuable method of applying metal layers to such substrates regardless of the geometry or conductivity of the substrate. This method is described, for example, by Frederic A. Lowenheim: "Modern Electroplating," John Wiley & Sons, New York, and by Heinz W. Dettner, J. Elze: Handbuch der Galvanotechnik Band II (Handbook of Electroplating) Carl Hauser Verlag, Munich.
In electroless metal plating, the surface of the substrate to be metal plated is provided with nucleating seeds of the noble metal. Conventionally, this is accomplished in particular by reacting compounds containing Sn.sup.2+ with compounds containing Pd.sup.2+ according to the equation EQU Sn.sup.2+ +Pd.sup.2+.fwdarw.Sn.sup.4+ +Pd
Palladium may be in the form of an aqueous PdCl.sub.2 solution or an organic palladium solution into which the substrate is dipped or with which the substrate is sprayed or printed. The palladium is bound to the substrate by adsorption. In addition to palladium, platinum is also used as a nucleating metal, but palladium is preferred because of its lower price. Then at least one metal is chemically deposited on the nucleation layer by reducing one or more salts of the metal(s) to be deposited.
One disadvantage of conventional method is that it is difficult to achieve a uniform nucleation. To ensure that the nucleation layer is closed, a large quantity of nucleating metal relative to the substrate surface area is necessary in any case. Furthermore, electroless metal plating of powders has not been known in the past. It has been determined that coverage was very irregular when using the conventional method of nucleation and a subsequent electroless metal plating.